­When a woman is moody, it's hormones. When a man is moody, it's work stress, or money problems, or just one of those days. Right?

Maybe not. An increasing amount of evidence points to an aging-related hormonal change in men that corresponds to the hormonal change in women known as menopause. Some call it "male menopause," which is not entirely accurate but still gets the point across: Much the way women's estrogen levels drop after a certain age, men's testosterone levels decrease with age. Testosterone is also known as androgen, and many doctors prefer the term "andropause" for this male condition.

Andropause and menopause are quite different, of course. In this article, we'll find out what "male menopause" really is and what men can do about it.

Menopause is a uniquely female condition -- it's the end of menstruation and everything else that entails. Menopause involves a sudden and dramatic decrease in estrogen that marks the end of a woman's ability to conceive a child. Men, on the other hand, do not lose the ability to father a child. Men in their 80s have fathered children. Sperm production doesn't stop, although sperm count in semen can decrease with age. Testosterone decreases very gradually, in the area of 1 percent per year starting around age 35 [source: MayoClinic].

Still, andropause is in many ways similar to menopause. While not all men are affected by the natural decrease in testosterone that comes with aging, lots are, including about 25 million men in the United States alone [source: Gearon]. The symptoms are remarkably similar to those experienced by women in menopause, including moodiness, fatigue, weight gain, depression, decreased sex drive, decreased muscle mass and bone loss.

­The symptoms can be quite pronounced, but andropause is still somewhat difficult to diagnose. For one thing, it can be mistaken for conditions like erectile dysfunction (ED) or the midlife crisis. Midlife crisis is a psychological phenomenon, not a physical one. And erectile dysfunction occurs when communication between particular nerves, arteries and muscles breaks down, as opposed to the slow, natural decrease in testosterone that characterizes andropause.